Network Working Group W. Kumari
Internet-Draft Google, Inc.
Intended status: Standards Track K. Sriram
Expires: January 4, 2018 US NIST
July 3, 2017
Deprecation of AS_SET and AS_CONFED_SET in BGP
draft-kumari-deprecate-as-set-confed-set-10
Abstract
RFC 6472 (i.e., BCP 172) recommends not using AS_SET and
AS_CONFED_SET in BGP. This document updates RFC 4271 and proscribes
the use of the AS_SET and AS_CONFED_SET types of the AS_PATH in
BGPv4. This is done to simplify the design and implementation of BGP
and to make the semantics of the originator of a route more clear.
This will also simplify the design, implementation, and deployment of
ongoing work in the Secure Inter-Domain Routing Working Group.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 4, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Kumari & Sriram Expires January 4, 2018 [Page 1]
Internet-Draft AS_SET, AS_CONFED_SET use deprecation July 2017
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
3. Recommendation to Network Operators . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 4
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
RFC 6472 (i.e., BCP 172) [RFC6472] makes a recommendation for not
using AS_SET and AS_CONFED_SET in BGP. This document advances the
recommendation to a standards requirement in BGP. It updates RFC
4271 and proscribes the use of the AS_SET and AS_CONFED_SET types of
the AS_PATH in BGPv4.
The AS_SET path segment type of the AS_PATH attribute (Sections 4.3
and 5.1.2 of [RFC4271]) is created by a router that is performing
route aggregation and contains an unordered set of Autonomous Systems
(ASes) that the update has traversed. The AS_CONFED_SET path type
([RFC5065]) of the AS_PATH attribute is created by a router that is
performing route aggregation and contains an unordered set of Member
AS Numbers in the local confederation that the update has traversed.
It is very similar to AS_SETs but is used within a confederation.
By performing aggregation, a router is, in essence, combining
multiple existing routes into a single new route. This type of
aggregation blurs the semantics of what it means to originate a
route. Said aggregation can therefore cause operational issues, such
as not being able to authenticate a route origin for the aggregate
prefix in new BGP security technologies (such as those that take
advantage of the "X.509 Extensions for IP Addresses and AS
Identifiers" [RFC3779]). This in turn would result in reachability
problems for the aggregated prefix and its components (i.e., more
specifics). Said aggregation also creates traffic engineering
issues, because the precise path information for the component
prefixes is not preserved.
Kumari & Sriram Expires January 4, 2018 [Page 2]
Internet-Draft AS_SET, AS_CONFED_SET use deprecation July 2017
From analysis of past Internet routing data, it is apparent that
aggregation that involves AS_SETs is very seldom used in practice on
the public network [Analysis] and, when it is used, it is usually
used incorrectly -- reserved AS numbers ([RFC1930]) and/or only a
single AS in the AS_SET are by far the most common case. Because the
aggregation involving AS_SETs is very rarely used, the reduction in
table size provided by said aggregation is extremely small, and any
advantage thereof is outweighed by additional complexity in BGP. As
noted above, said aggregation also poses impediments to
implementation of said new BGP security technologies.
In the past, AS_SET had been used in a few rare cases to allow route
aggregation where two or more providers could form the same prefix,
using the exact match of the other's prefix in some advertisement and
configuring the aggregation differently elsewhere. The key to
configuring this correctly was to form the aggregate at the border in
the outbound BGP policy and omit prefixes from the AS that the
aggregate was being advertised to. The AS_SET therefore allowed this
practice without the loss of BGP's AS_PATH loop protection. This use
of AS_SET served a purpose that fell in line with the original
intended use. Without the use of AS_SET, aggregates must always
contain only less specific prefixes (not less than or equal to), and
must never aggregate an exact match.
2. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Recommendation to Network Operators
Operators MUST NOT generate any new announcements containing AS_SETs
or AS_CONFED_SETs. If they have already announced routes with
AS_SETs or AS_CONFED_SETs in them, then they MUST withdraw those
routes and re-announce routes for the component prefixes (i.e., the
more-specifics of the previously aggregated prefix) without AS_SETs
or CONFED_SETs in the updates. This involves undoing the aggregation
that was previously performed (with AS_SETs/CONFED_SETs), and
announcing more specifics (without AS_SETs/CONFED_SETs). Route
aggregation that was previously performed by proxy aggregation (i.e.,
without the use of AS_SETs) is still possible under some conditions.
As with any change, the operator should understand the full
implications of the change.
It is worth noting that new technologies (such as those that take
advantage of the "X.509 Extensions for IP Addresses and AS
Identifiers" [RFC3779]) might not support routes with AS_SETs/
Kumari & Sriram Expires January 4, 2018 [Page 3]
Internet-Draft AS_SET, AS_CONFED_SET use deprecation July 2017
AS_CONFED_SETs in them, and may treat as infeasible routes containing
them. Future BGP implementations may also do the same. It is
expected that, even before the deployment of these new or future
technologies, operators may filter routes with AS_SETs/AS_CONFED_SETs
in them. Other than making that observation, this document is not
intended to make any recommendation for how an operator should behave
when receiving a route with AS_SET or AS_CONFED_SET in it. This
document's focus is entirely on the sender side, as discussed in the
preceding paragraph.
4. IANA Considerations
This document requires no IANA actions.
5. Security Considerations
This document obsoletes the use of aggregation techniques that create
AS_SETs or AS_CONFED_SETs. Future work, intended for securing BGP,
may update the protocol to remove support for the AS_SET and
AS_CONFED_SET path segment type of the AS_PATH attribute. This
future work will remove complexity and code that are not exercised
very often, thereby decreasing the attack surface.
6. Acknowledgements
The authors would like to thank Tony Li, Randy Bush, John Scudder,
Curtis Villamizar, Danny McPherson, Chris Morrow, Tom Petch, and Ilya
Varlashkin, as well as Douglas Montgomery, Enke Chen, Florian Weimer,
Jakob Heitz, John Leslie, Keyur Patel, Paul Jakma, Rob Austein, Russ
Housley, Sandra Murphy, Steve Bellovin, Steve Kent, Steve Padgett,
Alfred Hoenes, Alvaro Retana, everyone in the IDR working group, and
everyone else who provided input.
Apologies to those who we may have missed; it was not intentional.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
Kumari & Sriram Expires January 4, 2018 [Page 4]
Internet-Draft AS_SET, AS_CONFED_SET use deprecation July 2017
7.2. Informative References
[Analysis]
Sriram, K. and D. Montgomery, "Measurement Data on AS_SET
and AGGREGATOR: Implications for {Prefix, Origin}
Validation Algorithms", SIDR WG presentation, IETF 78,
July 2010, .
[RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation,
selection, and registration of an Autonomous System (AS)",
BCP 6, RFC 1930, DOI 10.17487/RFC1930, March 1996,
.
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779,
DOI 10.17487/RFC3779, June 2004,
.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
.
[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
System Confederations for BGP", RFC 5065,
DOI 10.17487/RFC5065, August 2007,
.
[RFC6472] Kumari, W. and K. Sriram, "Recommendation for Not Using
AS_SET and AS_CONFED_SET in BGP", BCP 172, RFC 6472,
DOI 10.17487/RFC6472, December 2011,
.
Authors' Addresses
Warren Kumari
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Phone: +1 571 748 4373
Email: warren@kumari.net
Kumari & Sriram Expires January 4, 2018 [Page 5]
Internet-Draft AS_SET, AS_CONFED_SET use deprecation July 2017
Kotikalapudi Sriram
US NIST
100 Bureau Drive
Gaithersburg, MD 20899
US
Phone: +1 301 975 3973
Email: ksriram@nist.gov
Kumari & Sriram Expires January 4, 2018 [Page 6]